1. The Field of the Invention
The present invention relates to an improved method for analyzing wireline well log data resulting in a better estimation of formation permeability and, in particular, to a method using neural networks for determining rock formation permeability from wireline well logs.
2. The Prior Art
The permeability of rock formations is one of the most important and essential fluid flow parameters associated with the characterization and production of a given hydrocarbon reservoir. The permeability of a reservoir is fundamentally a measure of the interconnectedness of the available porosity which determines how easily fluid can pass through it. Permeability tends to be a function of the fluid type, pore size and distribution, flow direction, facies type, shale content, and hererogeneties such as non-connecting vugs and fractures. Permeability can also be highly variable, both vertically and horizontally. The importance of permeability to the oil and gas industry is demonstrated by its use as a parameter which determines whether or not a well should be completed for hydrocarbon production. Permeability is also critical in overall reservoir management and development, i.e. for choosing optimal drainage points, calculating production rates, determining completion and perforation intervals, designing enhanced oil recovery patterns, and evaluating injection conditions.
Many equations (Table 1) and statistical techniques have been developed to predict formation permeability from wireline logs or log-derived results, such as total porosity and irreducible water saturation. However, not one of these proposed techniques can be universally applied since a particular relationship in one oil field or geological formation cannot be extended to other oil fields. Also, these empirical relationships, even within a particular geologic regime, do not adequately solve for permeability when compared to the available core data. This may be due to the simplifying assumptions which are made about the relationship between reservoir porosity, irreducible water saturation and permeability; or it may be due to the fact that all of the logging measurements and their interrelationships are not being considered in these equations. Whatever the case, log-derived permeability has to-date been inadequate and, as a result, measured core permeability still remains the industry standard used to characterize hydrocarbon reservoirs. There is however, a problem in depending on core permeability as an input to reservoir description. Cores are very expensive to acquire and are not always readily available. Thus, if an accurate way of deriving permeability from wireline logs could be developed, it would be a very valuable tool in reservoir analysis and the development of petroleum reserves.
TABLE I ______________________________________ Tixier Equation ##STR1## Kozeny-Carman Equation ##STR2## Timur Equation ##STR3## Coates Equation ##STR4## Coates-Dumanoir Equation ##STR5## ______________________________________